Lithographic printing methods using plates whose surface contains light reacted materials are known. One type of printing falling under this general classification involves the use of a photohardenable material which is soluble in certain solvents in the uncured state and insoluble in the solvent in the hardened state. The material is uniformly applied to a printing plate in the form of a thin layer. Exposing the layer to activating radiation causes it to harden in the exposed areas so that the non-exposed areas can be dissolved away thereby forming an etch resist. Exemplary of patents disclosing such a method is U.S. Pat. No. 1,574,378 in which gelatin is the layer forming material and the solvent is water.
U.S. Pat. No. 3,010,390 discloses a method of preparing a printing master which involves:
A. PROVIDING A HYDROPHILIC PRINTING SURFACE UNIFORMLY COVERED WITH A LAYER OF A HYDROPHOBIC MATERIAL OVER WHICH IS PLACED A SECOND SURFACE WHICH HAS A GREATER AFFINITY FOR THE HYDROPHOBIC MATERIAL IN ITS UNSENSITIZED STATE THAN DOES THE PRINTING SURFACE;
B. SELECTIVELY EXPOSING THE HYDROPHOBIC MATERIAL TO RADIATION TO RENDER IT HYDROPHILIC AND THEREBY CAUSE IT TO HAVE A GREATER AFFINITY FOR THE PRINTING SURFACE THAN THE SECOND SURFACE IN THE EXPOSED AREAS; AND
C. SEPARATING THE PRINTING SURFACE FROM THE EXPOSED HYDROPHILIC MATERIAL WHEREBY THOSE PORTIONS OF THE MATERIAL WHICH HAVE BEEN EXPOSED "STICK" TO THE PRINTING SURFACE TO PROVIDE A PRINTING MASTER HAVING THE MATERIAL ON ITS SURFACE IN IMAGEWISE CONFIGURATION.
It would be desirable, and it is an object of the present invention to provide a novel driographic imaging method which employs an ink whose viscosity is reduced by exposure to high energy electromagnetic radiation.
A further object is to provide such a process in which the ink comprises a photodegradable polymer.
An additional object is to provide such a process which is adaptable to a cyclic printing operation.